The present invention relates to a document reproduction machine such as a xerographic copier or scanner/printer and, more particularly, to such a machine having an enhanced capability for copying or scanning multi-page originals such as bound books.
In prior art reproduction machines, the copying of multi-page originals such as bound books presents a problem in that it is difficult to adequately copy the information adjacent the binding area. The "problem" is actually a series of problems all associated with the fact that pages being copied begin to lift away from the object plane (the document platen), with the lift increasing in the direction of the central binding area. This lift causes the following problems: (1) the projected image becomes increasingly out of focus; (2) the illumination becomes less than optimum in the spine area; and (3) angular misalignment of the principal projected ray at the image plane.
The above problems have been addressed in various ways in the prior art. A common "brute force" approach is to press the page or pages to be copied against the surface of a platen, U.S. Pat. No. 4,716,439 discloses one such arrangement However, as shown, for example, in FIG. 1 of the U.S. Pat. No. 4,716,839, portions of the pages adjacent the binding area still remain a short distance above the platen surface. Consequently, the information contained in these portions is out of focus on the photosensitive recording medium (and hence on the output sheet). Attempts to press the binding area closer to the platen can result in breaking the binding of the book.
Another solution to the above problem is to modify the platen to have a sloping edge portion whereby the bound part of a book is placed in a corner position so that the entire surface of the page being copied is in intimate contact with the platen surface. An example of such a system is disclosed in U.S. Pat. No. 3,775,008. These systems have several disadvantages; the magnification range is limited because of restriction on scan component movement encountering the sloping corner edge. Also operability and production are limited by the inability to employ a "split scan" scanning system which allows that both pages of a book be placed on the platen and scanned without repositioning.
According to the present invention, there is provided a scanning system which can scan documents in a normal document scan mode, but which has the added capability of scanning bound books in a book scan mode. In the book scan mode, a page height, detector mounted on the scan carriage, is activated at start of scan. In a first embodiment, the scan mechanism is moved through a pre-scan excursion whereby the detector detects and measures the deviation of the book pages from the horizontal platen plane. This deviation distance, which increases from the outer edges towards the center of the book is detected and converted into a series of analog output signals which, in turn, are used to provide corrective signals to components of the imaging system. In other words, scan speed is adjusted to develop the "true length" of the curved page, conjugate correction signals are sent to adjust for the out-of-focus and object conjugate length changes. Correction signals are also sent to the illumination lamp power supply to adjust illumination levels. A fourth correction signal is used to pivot the scan mirror so as to correct for the angular misorientation of the principal object ray. More particularly, the invention relates to an imaging system for forming an image on a photosensitive image plane of an object placed on a platen, said object having at least some areas out of physical contact with said platen by some distance .DELTA.z, the imaging system comprising: a scan mirror and scan illumination means mounted for parallel movement beneath said platen, optical detection means mounted for movement with said scan illumination means, said detection means adapted to generate a signal representative of .DELTA.z, and a microprocessor controller means for receiving said signals generated by said detector means and for generating output signals to correct for at least conjugate length changes in said imaging system created by said .DELTA.z distance.